Thrombin is the key serine proteinase of the coagulation cascade and, therefore, a suitable target for inhibition of blood coagulation. An extract of Amanita virosa considerably inhibited thrombin (48%), but showed no inhibitory activity on trypsin. On the basis of inhibition selectivity between thrombin and trypsin and potency of thrombin inhibition, A. virosa constitutes a good starting material for the isolation of further compounds that are active against thrombin. Bioassay oriented fractionation of the extract of A. virosa led to the isolation of a complex mixture of triglycerides (TGs), monoacylglycerols (MAGs), free fatty acids (FAs) and ergosterol. The structures of the isolated lipids metabolites were determined on the basis of chemical and spectroscopic evidences.